Method of making cathode ray tube internal shields

ABSTRACT

An internal magnetic shield of generally truncated pyramidal shape conforming generally to the inner wall of the funnel of a rectangular shadow mask type color picture tube is made up of four pre-annealed trapezoidal pieces of magnetic sheet metal assembled and attached together by overlapping flanges integral with the non-parallel sides of the pieces. The larger end of the shield is attached to the shadow mask frame by integral flanges on the long sides of the trapezoidal pieces. The sheet metal of the shield is annealed either before or after being formed into the trapezoidal pieces, but before assembly and attachment of the pieces together.

nited States Patent [191 Shrader l [54] METHOD OF MAKING CATHODE RAY TUBE INTERNAL SHIELDS I Related U.S,l Application Data [62] Division of Ser. No. 95,779, Dec. 7,

1970, abandoned.

[52] Us. ci 2st/25.14, 313/85, 313/313 [5l] Int. CI. H Olj 9/00 [58] Field of Search 29/25.13, 25.14; 313/64, 313/85, 85 S, 92 B, 313; 315/8; 178/7.82

[56] References Cited UNITED STATES PATENTS 3,549,932 12/19701 Lindt-imam,...A ..313/85 3,564,329 10/1968 Uetz, ..3l3/64UX l [4 5] July 9, i974 Primary Examiner-Roy Lake Assistant Examiner-J. W. Davie Attorney, Agent, or Firm-Glenn H. Bruestle; Dennis H. lrlbeck [57] ABSTRACT An internal magnetic shield of generallytruncatedpyramidal shape conforming generally to the inner wall of the funnel of a rectangular shadow mask type color picture tube is made up of four pre-annealed trapezoidal pieces of magnetic sheet metal assembled` and attached together by overlapping flanges .integral with the non-parallel sides of the pieces. The larger end'ot` the shield is attached to the shadow mask frame by integral flanges on the long sidesl of the trapezoidal pieces. The sheet metal of the shield is annealed either before or after being formed into the trapezoidal pieces, but before assembly and attachment of the pieces together.

2 Claims, 5 Drawing Figures PMENTEU JUL 91974 SHEE 2 BF 2 R m WL W Terry M072 roe Slzmder METHOD F MAKING CATHODE RAY TUB INTERNAL SHIELDS This is a division, of application Ser. No. 95,779, filed Dec. 7, 1970, now abandoned.

BACKGROUNDv oF THE INVENTION The present invention relates to an improvement in cathode ray tubes, such as color picture tubes, wherein vthe position of the electron beam spot on the. screen is critical, and is affected by stray magnetic fields in the beam path. For example, in a shadow mask type color tube wherein a plurality (usually three) of convergent electron beams are projected through a multiapertured color selection shadow mask to a mosaic screen along beam paths such that each beam impinges uponV and excites only one of the (three) kinds of color phosphor elements in the screen, the color phosphor elements are` usually located on the faceplate during manufacture by a method (e..g., by photoprinting through the mask) which' does not involve any mag'- netic field. Thus, when the finished tube is operated in the presence of a magnetic field, such as the earths field, undesirable misregister of the beam spots and color phosphor elements is produced. For this reason, such'color tubes, especially those with a high 'deflection angle e.g., 110), are'sometimes provided with an internal magnetic shield mounted within the envelope funnel and extending along at least the forward half thereofnearest the maskfand screen. Heretofore, such internal shields have been made in one piece by drawing a flat sheet of magnetic sheet metal, such as coldrolled steel, into a frustum of a cone or pyramid to conform to the inner wall of the envelope funnel. Particularly in the case of rectangular tubes where the forward end of the funnel has the general shape of a truncated pyramid, this drawing operation work hardens the ma 2 FIGS. l4 and 5 are side and end elevation-views of the magnetic shield of FIG. 3. t

- For example, the present invention is illustrated in FIGS. land 2 as incorporated in a rectangular color picture-tube l comprising a glass envelope 3 including a panel 5, afunnel7 and a neck 9. The funnel 7 comprises a small circular end joined to the neck 9 and a large end of generally truncated pyramidal shape frit sealed to the panel 5. The panel Scomprises a generally rectangular faceplate 11 and a peripheral side wall 13. A mosaic color phosphor screen 15 is disposed on the inner surface of the faceplate 1l. An electron gun structure 17 is mounted in the neck 9 to project three convergent electron beams toward the screen l5. The tube 1 is adapted tobe used with a magnetic deflection yoke 19 for scanning the electron beams over the surface of the screen. A multi-apertured color selection shadow mask 21 is mounted in predetermined spaced relation adjacent to the screen l5.` The `mask 21 includes a mounting frame v23 comprising `an axiallyl l v A four-piece magnetic shield is disposed within However, theannealing of 'finished one-piece shields would Vrequire large separate stacking fixtures and a large'annealing oven, which would be very expensive.

SUMMARY oF THE iNvENTioN The internal magnetic shield iri a cathode ray tube is made up of four pre-annealed trapezoidal pieces or plates of magnetic sheet metal assembled and attached together along the non-parallel sides thereof. Preferably, the non-parallel sides of each pair of adjacent pieces are attached to each other by means of overlapping flanges integral with the pieces, and the larger end of the shield is mounted on an electrode, e.g., a shadow mask frame ina color picture tube, in the envelope by means of integralflanges on the long sides of the trapezoidal pieces. 7

vBRIEF DEsCRiPrioN oF THE DRAWING the larger end of the funnel 7 and supported by the lar flanges 43 on the non-parallel sides of the adjacent plates 39, in overlapping relationship. After assembly of thefour plates 37 and 39 as shown -in` FIG. 3, the overlapping flanges 41 and 43 are attached together, as

by welding or riveting. The plates 37 and 39 are formed along their longer sides with integral'flanges 45 and 47, respectively, bent to extend parallel to the longitudinal axis of the shield y35, as shown in FIGS. 4 and 5. The shield 35 is mounted on the mask frame 23 by telescoping the flanges 45 and 47 over the frame 23 and attaching the flanges to the frame, as by welding. The flanges 45 and 47 are formed with notches 49 to clear the mounting springs 31 (or attaching plates).

The plates 37 and 39 are cut from magnetic sheet metal, such as alurninum-killed-steel (AKS) having a thickness of 4 to 8 mils, and stamped to form the integral flanges 41, 43, 45 and 47. The formed plates are preferably annealed afterv the stamping operation. However, the sheet metal may be annealed before the plates are formed, since the small amount of bending involved in the formation of the flanges has only a small effect on the magnetic properties of the finished shield 35. The annealing can be done after the flanges are formed at acomparitively low cost, since the separate plates 37 and 39 are relatively flat, and hence, do not require a large annealing oven.

The presently planned use of the invention is in shadow mask color picture tubes, as described above. However, the improved magnetic shield can be used in other types of color picture tubes having mosaic screens, or in oscillograph tubes, for example, in which the instantaneous position of the beam spot on the phosphor screen is critical.

I claim:

l. The method of making a funnel-shaped internal magnetic shield for a rectangular cathode ray tube having a funnel portion of generally truncated pyramidal shape, comprising the steps of: l

a. forming two pairs of trapezoidal plates of magentic sheet metal having dimensions such that when the a and attachingsaid non-parallel sides of adjacent y plates to each other. 2. The method of claim l, wherein each of said plates is formed in step a with integral flanges on said nonparallel sides, adapted to overlap the flanges of the adjacent plates when assembled together. 

1. The method of making a funnel-shaped internal magnetic shield for a rectangular cathode ray tube having a funnel portion of generally truncated pyramidal shape, comprising the steps of: a. forming two pairs of trapezoidal plates of magentic sheet metal having dimensions such that when the magnetic plates are assembled together with their non-parallel sides fitted together they will form a truncated pyramid similar to the inner wall of said funnel portion; b. annealing said trapezoidal plates to optimize the magnetic properties; and c. then assembling said plates together as recited in a and attaching said non-parallel sides of adjacent plates to each other.
 2. The method of claim 1, wherein each of said plates is formed in step a with integral flanges on said nonparallel sides, adapted to overlap the flanges of the adjacent plates when assembled together. 